Re: [patch 1/6] mmu_notifier: Core code

Christoph Lameter
2008-02-16T19:31:21Z

On Sat, 16 Feb 2008, Andrew Morton wrote:

> "looks good" maybe. But it's in the details where I fear this will come
> unstuck. The likelihood that some callbacks really will want to be able to
> block in places where this interface doesn't permit that - either to wait
> for IO to complete or to wait for other threads to clear critical regions.

We can get the invalidate_range to always be called without spinlocks if
we deal with the case of the inode_mmap_lock being held in truncate case.

If you always want to be able to sleep then we could drop the
invalidate_page() that is called while pte locks held and require the use
of a device driver rmap?

> >From that POV it doesn't look like a sufficiently general and useful
> design. Looks like it was grafted onto the current VM implementation in a
> way which just about suits two particular clients if they try hard enough.

You missed KVM. We did the best we could being as least invasive as
possible.

> Which is all perfectly understandable - it would be hard to rework core MM
> to be able to make this interface more general. But I do think it's
> half-baked and there is a decent risk that future (or present) code which
> _could_ use something like this won't be able to use this one, and will
> continue to futz with mlock, page-pinning, etc.
>
> Not that I know what the fix to that is..

You do not see a chance of this being okay if we adopt the two measures
that I mentioned above?